Core issue
CPU utilization increases when the Open Shortest Path First (OSPF) process is enabled on PIX. The problem occurs when two OSPF processes, namely, OSPF Hello and OSPF Router, continuously poll the OSPF database.
Resolution
Currently, no workaround is available. However, this issue is resolved in PIX versions 7.0(3.9),7.1(1),7.1(0.2).
For more information, refer to Cisco bug ID CSCei20466.